Open a full-screen preview when tapping a gallery item

Tapping a gallery tile/row opens the existing media preview scoped to that gallery's attachments, paging between them. Introduces a typed MediaPreviewItemID (replacing the stringly-typed preview identifier) and a gallery-scoped TimelineMediaPreviewDataSource; the tap routes through TimelineInteractionHandler/TimelineViewModel. Non-previewable (.other) items are skipped without shifting the tapped index.

Co-authored-by: svetoslav.mitov <svetoslav.mitov@sportinno.com>

just use id instead of previewID

removed horrible multiline ternary

pr suggestions

remove redundant code

remove empty caption display + gallery uses the appropriate media timeline actions

ElementX/Sources/Screens/FilePreviewScreen/TimelineMediaPreviewModels.swift

@@ -15,8 +15,21 @@ enum TimelineMediaPreviewViewModelAction: Equatable {
     case dismiss
 }
 
+/// Identifies a media preview item — either a whole timeline item or a single gallery attachment.
+enum MediaPreviewItemID: Hashable {
+    case timelineItem(TimelineItemIdentifier.EventOrTransactionID)
+    case galleryItem(GalleryItemID)
+    
+    /// Identifies by event/transaction ID only, since the unique ID differs across timelines
+    /// and matching must survive rebuilding a filtered timeline to fetch the other media.
+    init(timelineItem: EventBasedMessageTimelineItemProtocol) {
+        guard let id = timelineItem.id.eventOrTransactionID else { fatalError("Virtual items cannot be previewed.") }
+        self = .timelineItem(id)
+    }
+}
+
 enum TimelineMediaPreviewDriverAction {
-    case itemLoaded(TimelineItemIdentifier.EventOrTransactionID)
+    case itemLoaded(MediaPreviewItemID)
     case showItemDetails(TimelineMediaPreviewItem.Media)
     case exportFile(TimelineMediaPreviewFileExportPicker.File)
     case authorizationRequired(appMediator: AppMediatorProtocol)